Until the end of 2022, the covers of the Journal of Comparative Physiology A remained the same for several issues. Starting with Issue 1 in 2023, we solicited a new cover picture for each issue. This enabled us to better align the cover and the content of the respective issue, especially in the case of special issues, which are dedicated to specific topics. Many of the cover images are provided by the authors of an article published in the respective issue. In these cases, the cover can serve as a powerful promotional tool to showcase the scientific — and often also the artistic — quality of the work. This applies not only to photographs (for a magnificent example see the cryo-Scanning Electron Micrograph of attachment pads on the legs of the ladybird beetle shown on the cover of Issue 2, 2023), but also to some truly superb pieces of art, such as the mixed-media composition painted in acrylic and based on a high-speed still image of a flying zebra finch recorded in a forward flight chamber (see cover of Issue 5, 2023). Readers can find these two covers and the stories behind them in full size and high resolution in the editorial by Zupanc (2023).

The custom covers provide us also with the opportunity to better highlight one of the core elements of our publishing philosophy — making available the journal as a premier platform for comparative physiological work. Over the last 100 years, the research published in the nearly 10,000 articles in the Journal of Comparative Physiology A has been based on over 1500 taxa from 17 phyla of the animal kingdom (Wagner et al. 2024). Yet, as much as we try to diversify the animal taxa displayed on the journal covers, they can never give us more than an incomplete idea of the actual taxonomic diversity represented by the work of the community of our authors.

Despite the obvious benefits of changing the covers with each issue, we also face several challenges. Of course, we always try to find an attractive picture that captures at least part of the message conveyed by the respective article or the special issue. However, by far not every attractive picture is suitable for a cover. Since font size and position of the masthead are fixed, but the pictures extend to this cover element, we must identify images in which the main subject shown in the picture does not interfere with the journal title. Unfortunately, few figures in articles published in the journal meet this requirement. We, therefore, work closely with authors to find or even create alternate images of similar content but different — suitable — format. Ideally, the main subject should cover the lower half of the image, while the background extends to the upper half. (In only one instance, we used AI technology to extend the background of an image to the area of the masthead; see cover of Issue 4, 2024, below.) If authors cannot provide a suitable image, then we turn to stock images — a time-consuming approach that often requires the screening of hundreds of photographs until one is found that is both scientifically sound and artistically suitable.

In the following, the cover images of the six issues of the Journal of Comparative Physiology A published in 2024 are shown (Figs. 1, 2, 3, 4, 5, 6). Two of them were special issues: Issue 2 was published in celebration of the 100th anniversary of the founding of our predecessor journal, the Zeitschrift für vergleichende Physiologie (whose first edition appeared in March 1924, hence our Centennial Issue was also published in March). Given the pioneering work on the behavior of bees of the journal’s co-founder and editor-in-chief, Karl von Frisch, the cover shows — what else? — a honeybee collecting nectar and pollen while visiting a flower plant (Fig. 2). The second special issue published in 2024 was titled A Clock for All Seasons. It contains an excellent collection of 19 articles on how circadian clocks adapt organisms to annual changes in the environment. Aptly, the editors chose for the cover of this special issue an image of migrating barnacle geese as an example of a seasonal migratory bird (Fig. 4). The other four issues published in 2024 are regular issues, and each of their covers highlights one specific original research article: A slaty-headed parakeet climbing a tree, highlighting the article by Young et al. (2024) (Issue 1; Fig. 1); a labeled type-1 omega neuron in the prothoracic ganglion of a bush-cricket, highlighting the article by Bayley and Hedwig (2024) (Issue 3; Fig. 3); a red-cheeked cordon bleu, highlighting the article by Rose et al. (2024) (Issue 5; Fig. 5); and larvae of the fruit fly Drosophila melanogaster forming a cluster for cooperative feeding, highlighting the article by Liao et al. (2024) (Issue 6; Fig. 6). Each of the legends for these figures also contains a short description of how the cover relates to the research presented in the respective article.

Cover of Issue 1 (2024). This cover photograph shows a slaty-headed parakeet (Psittacula himalayana) climbing a tree near its nest in Thandiani in the Abbottabad District of Pakistan. Like other parrots, this species incorporates its tail and craniocervical system (comprising musculoskeletal components of the head and neck) into the gait cycle during vertical climbing. The tail is braced against the trunk, thereby opposing the backward torque of the body. The craniocervical system is co-opted into a ‘third limb’. As such, it generates comparable magnitudes of propulsive and tangential forces to the hindlimb. The biomechanical analysis by Melody W. Young, Clyde Webster, Daniel Tanis, Alissa F. Schurr, Christopher S. Hanna, Samantha K. Lynch, Aleksandra S. Ratkiewicz, Edwin Dickinson, Felix H. Kong, and Michael C. Granatosky in this issue shows that the activation of the tail and the craniocervical system are rather independent of each other. Tail usage is already ubiquitous at inclination angles of surfaces at 45°, while the craniocervical system becomes prevalent only at angles greater than approximately 65°. Notably, parrots appear to abstain from the usage of wings for ascending vertical substrates. For further information see Young et al. (2024). (Image courtesy and copyright: Jrs Jahangeer/Shutterstock; text: Günther K.H. Zupanc, Michael C. Granatosky, Melody W. Young.)

Cover of Issue 2 (2024). Honeybee (Apis mellifera) collecting nectar and pollen while visiting common lavender (Lavandula angustifolia). Honeybees have played an important role in the 100 years of history of the Journal of Comparative Physiology A. Its cofounder and first editor-in-chief, Karl von Frisch, is best known for his discovery of the dance language of bees. Two women scientists, Ruth Beutler and Ingeborg Beling, who received their PhD degrees under his mentorship, contributed significant research on honeybees. The life and work of each of these women are described in this special issue commemorating the 100th anniversary of the Journal of Comparative Physiology A (see the editorial by Zupanc (2024)). Beutler was the first who identified the honey stomach as the site where bees store glucose; and she was the first who determined the blood sugar concentration in bees by employing a new method she had developed earlier. Beling was the first who succeeded in experimental demonstration of time memory in honeybees, a capability that they use for optimizing foraging when they visit flowers. This landmark discovery made her an early pioneer of chronobiology. (Image courtesy and copyright: ETgohome/Shutterstock; text: Günther K.H. Zupanc.)

Cover of Issue 3 (2024). Omega neurons 1 (ON1) are a bilateral pair of auditory interneurons in the prothoracic ganglion of bush-crickets. These interneurons respond to a broad range of sound frequencies but are most sensitive to the calling song of conspecific males. The image shows the structure of an ON1 of the bush-cricket Mecopoda elongata. The neuron was filled by intracellular iontophoretic injection of the dye Alexa-568 and its structure revealed after fixation and tissue clearing. The image was taken with a wide-field microscope using excitation and emission filters as detailed in Bayley and Hedwig (2024). Anterior is to the bottom of the image, dendrites are on the right and axonal arborizations are to the left of the midline. (Image courtesy and copyright: Timothy Bayley, Berthold Hedwig; text: Berthold Hedwig, Timothy Bayley, Günther K.H. Zupanc.)

Cover of Issue 4 (2024). The survival of species living at high latitudes depends on timely preparation for the coming seasons. One strategy to survive harsh winters is to migrate to warmer regions in the fall, long before winter sets in. Another strategy is to go into a state of dormancy or hibernation, also known as diapause in insects. As ambient temperature is not a reliable predictor of the coming season, most organisms measure the length of the day using their circadian clock as an internal time reference. The special issue A Clock for All Seasons encompasses work that investigates the role of the circadian clock in adapting to the regularly occurring seasonal changes in plants and animals (see the editorial by Helfrich-Förster and Rieger (2024)). The editors chose an image of migrating barnacle geese (Branta leucopsis) as an example of seasonal migratory birds that breed in high latitudes (Greenland, Svalbard, northern Siberia) and winter in Europe (Ireland, Scotland, North Sea coast). The picture was taken in Germany. In the upper portion of the cover image, blue-sky background was added, using the Crop tool and Generative Expand in Adobe Photoshop 2024. (Image courtesy and copyright: Pascal Halder/istockphoto; text: Charlotte Helfrich-Förster.)

Cover of Issue 5 (2024). The image shows a red-cheeked cordon bleu (Uraeginthus bengalus) in Gondar, Ethiopia. The red cheek plumage identifies the bird in this photograph as a male. In this estrildid finch, not only males but also females produce extensive song. Historically, research has focused heavily on male song, and little work has been done on species with sex-similar song production rates. In their study published in Issue 5, Evangeline M. Rose, Chelsea M. Haakenson, Aliyah Patel, Shivika Gaind, Benjamin D. Shank, and Gregory F. Ball examined some of the physiological factors that control song behavior in both sexes. Notably, the authors observed no significant sex differences in song production rates, nor in circulating levels of testosterone and progesterone. Likewise, they failed to find significant differences in cell densities in the song-system nuclei HVC and the robust nucleus of the arcopallium, and they detected only minor sex differences in the volume of HVC. Finally, as revealed by the authors, the levels of motor-driven immediate early gene expression are similar in males and females after song production. For further information see Rose et al. (2024). (Image courtesy and copyright: Artuch/Shutterstock; text: Günther K.H. Zupanc.)

Cover of Issue 6 (2024). The photograph shows a cluster of larvae of the fruit fly (Drosophila melanogaster). The larvae form such clusters for cooperative feeding by exhibiting synchronized digestion and mixing of external food. It is thought that this cooperation provides fitness benefits to the emerging adults. However, the benefits are offset if too many individuals aggregate, thereby leading to a depletion of resources. Thus, there is an optimal density of animals at which cooperation is maximally beneficial. The benefit, reflected by a positive correlation between population density and individual fitness, is referred to as the ‘Allee effect’. It is named after Warden Clyde Allee (1885–1955), a zoologist who spent a major part of his career at the University of Chicago and dedicated most of his research efforts to the study of animal aggregation and cooperation. In their paper published in Issue 6, Amy Liao, Christy Qian, Sepideh Abdi, Peyton Yee, Sean Michael Cursain, Niav Condron, and Barry Condron examined how various population parameters impact the Allee effect by employing different strains of Drosophila, including larvae that cannot exodigest or cluster. These ‘cheaters’ gain greatly from the hosts but, paradoxically, so do the hosts. This finding indicates that clustering of Drosophila larvae and the benefits of this behavior are dependent on more than just the contribution to exodigestion. Thus, this phenomenon is more complex than previously assumed. For further information see Liao et al. (2024). (Image courtesy and copyright: Barry G. Condron; text: Günther K.H. Zupanc.)

Enjoy the covers and the stories behind them— and please contact us when you have an idea for a great cover!